Monday, November 01, 2010

Building a composting toilet with a urine separator by Walt Barrett

Composting Toilet by Walt Barrett
I promised that I would write an article about the composting toilets that we build, so here it is. It includes my idea of a sliding adjustable urine separator.
The customers that we have using this toilet are very happy with it.
One of the main killers in the world is contaminated drinking water. In third world counties people can be very careless about where they dispose of their fecal matter. The sad results are disease followed by death usually from Cholera! This is because the runoff from this human waste is polluting the streams, rivers and lakes in those countries. We don't need fancy units to solve this problem. All we need is to convince people to properly dispose of their own waste in a composter protected from the rain to prevent runoff. You would think that at least in the last 5000 years the could have learned that.
Well this is our version of the composting toilet for the off grid home so that you can have the indoor convenience and a safe, economical disposal method for human waste.

Please read this and don't skip any steps or you will ruin the project.
It's tricky in a couple of spots to get the unit in square.
This is a relatively simple unit to build and I am just going to take you through all the steps right now. My son John and I sketched out the design we had been discussing for a practical composting toilet, and figured out the dimensions that we needed to fit the actual standard toilet seat and make room below for the two plastic collection bins and the vent stack. We also wanted to build as many units as possible from a single sheet of decent quality 3/4 inch plywood. While at the Home depot we had a 4' x 8' sheet of plywood ripped into three long pieces approximately 16” wide each. Those cuts must be exact so all three lengths have the same width. Home Depot or Lowe's will use a panel cutting saw which will make perfect cuts if the sheet is measured correctly. Note that due to the width of the saw blade the width will be slightly under 16” . You can compensate for this on assembly by assembling the pieces so that the box is slightly narrower than 16”
Next we cut two 16” wide X 16 inches high for the two (2) end pieces.
That leaves the two sides, the bottom, and the top. Now this is where you have to be careful. Look carefully at the construction of the box in the photos. We cut the two side pieces 22 inches x 16 inches high. That left the top and the bottom pieces which we cut
23 ½ ” inches long. Now we have all the pieces and that leaves us to position the store bought toilet seat and trace the hole in the top cover. I use the larger and better oval type toilet seat that fits the better quality toilets that you find in better homes and all commercial applications. They are much more comfortable for adults. I then drill a 3/8” hole for the saber saw, and cut out the hole in the top of the box. Make sure the hole is back far enough to accommodate the urine collector drain bin.
Now let's stop right here for a minute and make a cutting schedule.
All pieces are ripped 16 inches wide. It allows you to get the most toilets from one sheet of ¾ inch plywood. So here is the schedule. ” = inches.
2 End Pieces 16” x 16”
2 Side pieces 22” x 16”
1 Bottom piece 23 ½” x 16”
1 Top piece 23 ½” x 16”
At this point it is best to sand, and clean all the pieces off with paint thinner. Because if you are going to stain your unit like we do here. You must stain before you start using the wood glue. If you don't stain first, wherever you get glue on the wood the stain will not take and it looks terrible.
After the stain is thoroughly dry I use a couple of brads on each end and lightly tack the four sides together while just sitting on the bottom piece just to check for fit, and using a large metal square I make sure it will square up in three directions. You could also measure diagonally from corner to corner for equal dimensions in two directions. Then set the top on Just to make sure it fits squarely.
Once you are satisfied with all of the workmanship and the fit of all the pieces, it's time for the permanent assembly. This is how we do it.
  1. Set the four sides that are lightly tacked together on your flat work bench surface.
  2. Remove one of the ends that you have tacked on and tap the finish nails that were holding it back away so that you can hammer them in again easily.
  3. Then run a thin bead of quality carpenters glue down just off center favoring the interior of the box. Do not use too much glue as it will squash out all over your finish. Thats why you always favor the inside edge. You cannot stain over excess glue blotches.
  4. Now careful pet the end cap back in place and nail it securely with six long finish nails on either side.
  5. Repeat the process on the opposite end.
  6. Next you run a bead of glue around the rim where the bottom of the box will be nailed.
  7. Set the bottom on and while someone helps to hold the box square you nail on the bottom using long finish nails about every four inches. It is very helpful if you nail a couple of cletes to hold the corners square while you nail your box together. Corner cletes on either end will also hold your box square while the glue is drying. If you have clamps, use them too get a tighter glue joint. You can also take a length of rope and wrap it around the box , make a loose knot, insert a length of stick and twist the rope until you get several pounds of pressure on your joints.
  8. Be sure to wash off any glue that squeezes out of the joints immediately.
That leaves us with the top which never gets fastened down because it has to lift on and off to remove both of the bins for cleaning etc. the lid is kept from sliding around by use four pieces of aluminum angle tacked inner the rim on the center of each side to provide a snug fit to the box. That way the lid is easily removed for cleaning purposes. See the photos for the aluminum pieces.
Now you have built a regular composting toilet without a urine separator. We got our plastic collection bins from Walmart. We purchased a smaller fairly deep bin for the urine collector. We got the fittings and clear plastic ½ inside diameter inch drain hose, and clamps from the plumbing department at the home depot. The drain hole goes out the side of the bin and box as high up as you can get it without kinking the hose and still get a good gravity feed to your exterior collection system. The brackets are made from the flat perforated metal plated to buy at the home depot that are use for building decks and joining pierces together for various construction projects. I bent then to the shape I wanted using my bench vise and a rubber mallet. Be careful for sharp metal edges! If you want a vent stack you can put it in one of the rear top corners or elbow out of one of the rear sides, or end. It the best way to go and add a solar vent fan too.
This is a pretty good project for a beginner, but believe me, Manufactured units go from $800.00 to $2,500.00 dollars, and thats a lot of money for a person on a budget. This unit will work just as well. Just keep a spray bottle around with a little bleach and water in it to freshen up the urine catcher after each use. You can cover the fecal matter after each use with any kind of dries vegetable matter, like saw dust, Pete moss. Dried leaves, dried grass etc. Just don't get bleach water in the composting material.
You can empty the compost into a barrel with a watertight lid on it. If you are going to introduce earthworms to the compost you have to keep it moist without drowning the worms.
Be sure to make provisions fore the composter to drain excess fluids into more compost beneath it. Never compost anything near your water supply. Keep the composter as far away from you well as possible. After a couple of years the compost will turn int rich black soil. Throw all of your table scraps into the outdoor composter too.
Well, I think I covered everything. If I didn't, I'm counting on you all to let me know.
© 2010 Walt Barrett